From MERV Ratings to Sizing: 4 Types of Furnace Air Filters You Should Know Furnace air filters accomplish two significant roles: maintaining your heating and cooling (HVAC) system and preserving the air quality in your home.  Furthermore, furnace filters act as the first line of defence, preventing dust, pollen, and... From MERV Ratings to Sizing: 4 Types of Furnace Air Filters You Should Know Furnace air filters accomplish two significant roles: maintaining your heating and cooling (HVAC) system and preserving the air quality in your home.  Furthermore, furnace filters act as the first line of defence, preventing dust, pollen, and...